VERY last resort: You'll ask a copyright holder for permission to upload their image.

Warning: This is complicated, time-consuming, and perhaps unlikely to work. You should first strongly consider uploading an image that is freely available according to the above scenarios. You also should consider simply linking to the image rather than embedding or uploading it.

When looking for images in Wikimedia Commons, search for a word (eg, brain), then browse a category (eg, Brain). In many cases, browsing a category will yield more results.

To make your image appear in an article: Add this code [[File:Image name|thumb|Caption]] where you want the image to appear.

Wikimedia Commons includes videos too. To make a video appear in an article: Add this code [[File:Example.ogg|frame|alt=Alternative text|Caption text]] where you want the image to appear. More advice at Help:Visual file markup